The amelogenin proteins have a fundamental role in development of normal dental enamel. Evidence for this comes from patients with mutations in the amelogenin (AMELX) gene, who have the enamel defect amelogenesis imperfecta (AI), and from Amelx null mice, which have a condition similar to the X-linked form of AI. Null and transgenic murine models that correspond to various types of AI identified in human patients have begun to reveal roles of both the normal and mutated enamel proteins. Mice null for matrix metalloproteinase-20 (MMP-20) also have an enamel defect similar to a human AI, due to deficiency in proteolytic processing of amelogenins and other enamel proteins during development. These animal models provide information concerning basic processes in human development because of similarities between rodent and human enamel proteins, mineral and dental development in general. In this competitive renewal application, we propose the following aims: (i) To analyze the rescued enamel phenotype in transgenic mice with an Amelx null genomic mutation to determine roles of the 180 and 59 amino acid amelogenin proteins, using light, scanning and transmission electron microscopy;(ii) To evaluate enamel thickness, structure and crystal dimensions and orientation in the Amelx null, MMP20 null, and Amelx null mice with normal and mutated amelogenin transgenes for fundamental information about the role of the amelogenin C-terminus in vivo;(iii) To determine the role of genetic background in the observed enamel phenotypic heterogeneity in null mice;and (iv) To use murine models with different classifications of enamel defects in an interdisciplinary approach to develop enamel bonding treatments for AI in patients with different enamel gene mutations. At the conclusion of this work, a better understanding of the function of individual amelogenins during enamel development, and insight into the role that other proteins play in disease severity, will lead to new treatments designed for individuals with different AI mutations. This combination of basic and clinical approaches will generate fundamental knowledge as well as translational application that will benefit the public by providing therapeutic approaches that correspond to genetic alterations, leading to improved dental/oral health. Project Narrative: Patients with defective enamel frequently have prolonged clinical treatment, pain and social anxiety because of the appearance of their teeth. An understanding of how inherited gene mutations cause enamel defects will lead to insight into how enamel develops and shed more light on how to prevent structural defects from developing. Mouse models mimic the human defects and can be used to correlate individual gene mutations with appropriate clinical intervention.